Actually, the really interesting thing about the Juggernauts is where they were going and what they were doing.
The Lucifer was one thing. It went straight for big population centers and destroyed them. The Sathanas however, as best as I can recall, only ever attacked GTVA military forces. Even then, they usually blew up one or two of whatever the biggest thing around was, and then left, even if there were other ships in the area. The Sathanas that takes down the Colossus, for example, leaves immediately afterwards, completely ignoring the other GTVA forces there.
Really, the only thing that really makes sense, from the Shivan perspective, was that their primary goal was to sever all links with Terran/Vasudan space while causing as few non-military casualties as they could. They identified the one system that linked into Shivan space (Capella), and assaulted military targets exclusively with sufficient force that the GTVA evacuated the system. Once that was underway, they blew up the star to completely eliminate any possible extended confrontation between themselves and the GTVA.
Think about it. They had dozens of Sathanas juggernauts. If their objective had been to lay waste, there's nothing the GTVA could have done to stop it. They would have flooded Capella with juggernauts, taken over all the jump nodes out of Capella AND their far sides, and turned any inhabited planets there into cinders, and the GTVA would have been completely helpless.
This was a defensive fight for the Shivans. THEY were trying to protect themselves from US. Nothing else really makes sense.
Anyway, back on topic, it doesn't seem likely that the GTVA would be building anything on the Colossus scale anytime soon. The NTF is gone, their fleet has been chopped way down, and they've got a LOT of star systems to patrol. The Colossus was built to be a fleet-buster, able to sail right into the middle of an enemy formation and lay waste in all directions. Right now, their primary enemies(pirates, rebels, mercenaries, etc) are going to small, scattered, and hard to pin down. What the GTVA is going to need first, and most desperately, is lots and lots of cruisers and corvettes just to keep sufficient military presence in their space to keep the peace.